thumb|400px|[[Church Father Saint Augustine was the first clear advocate of just-war theory.]]
The just war theory () is a doctrine, also referred to as a tradition, of military ethics that aims to ensure that a war is morally justifiable through a series of criteria, all of which must be met for a war to be considered just. It has been studied by military leaders, theologians, ethicists and policymakers. The criteria are split into two groups: ("right to go to war") and ("right conduct in war"). There have been calls for the inclusion of a third category of just war theory (jus post bellum) dealing with the morality of post-war settlement and reconstruction. The just war theory postulates that war, while it is terrible but less so with the right conduct, is not always the worst option, but justifiable when justice is an objective of armed conflict. Important responsibilities, undesirable outcomes, or preventable atrocities may justify war. A few, such as Rousseau, argue for insurrection against oppressive rule.
The historical aspect, or the "just war tradition", deals with the historical body of rules or agreements that have applied in various wars across the ages. The just war tradition also considers the writings of various philosophers and lawyers through history, and examines both their philosophical visions of war's ethical limits and whether their thoughts have contributed to the body of conventions that have evolved to guide war and warfare.
In the twenty-first century there has been significant debate between traditional just war theorists, who largely support the existing law of war and develop arguments to support it, and revisionists who reject many traditional assumptions, although not necessarily advocating a change in the law.
Origins
Ancient Egypt
A 2017 study found that the just war tradition can be traced as far back as to Ancient Egypt. Egyptian ethics of war usually centered on three main ideas, these including the cosmological role of Egypt, the pharaoh as a divine office and executor of the will of the gods, and the superiority of the Egyptian state and population over all other states and peoples. Egyptian political theology held that the pharaoh had the exclusive legitimacy in justly initiating a war, usually claimed to carry out the will of the gods. Senusret I, in the Twelfth Dynasty, claimed, "I was nursed to be a conqueror...his [Atum's] son and his protector, he gave me to conquer what he conquered." Later pharaohs also considered their sonship of the god Amun-Re as granting them absolute ability to declare war on the deity's behalf. Pharaohs often visited temples prior to initiating campaigns, where the pharaoh was believed to receive their commands of war from the deities. For example, Kamose claimed that "I went north because I was strong (enough) to attack the Asiatics through the command of Amon, the just of counsels." A stele erected by Thutmose III at the Temple of Amun at Karnak "provides an unequivocal statement of the pharaoh's divine mandate to wage war on his enemies." As the period of the New Kingdom progressed and Egypt heightened its territorial ambition, so did the invocation of just war aid the justification of these efforts. The universal principle of Maat, signifying order and justice, was central to the Egyptian notion of just war and its ability to guarantee Egypt virtually no limits on what it could take, do, or use to guarantee the ambitions of the state.
In Sikhism, the term dharamyudh describes a war that is fought for just, righteous or religious reasons, especially in defence of one's own beliefs. Though some core tenets in the Sikh religion are understood to emphasise peace and nonviolence, especially before the 1606 execution of Guru Arjan by Mughal Emperor Jahangir, military force may be justified if all peaceful means to settle a conflict have been exhausted, thus resulting in a dharamyudh.
East Asian
Chinese philosophy produced a massive body of work on warfare, much of it during the Zhou dynasty, especially the Warring States era. War was justified only as a last resort and only by the rightful sovereign; however, questioning the decision of the emperor concerning the necessity of a military action was not permissible. The success of a military campaign was sufficient proof that the campaign had been righteous.
Japan did not develop its own doctrine of just war but between the 5th and the 7th centuries drew heavily from Chinese philosophy, and especially Confucian views. As part of the Japanese campaign to take the northeastern island Honshu, Japanese military action was portrayed as an effort to "pacify" the Emishi people, who were likened to "bandits" and "wild-hearted wolf cubs" and accused of invading Japan's frontier lands.
Ancient Greece and Rome
The notion of just war in Europe originates and is developed first in ancient Greece and then in the Roman Empire.
It was Aristotle who first introduced the concept and terminology to the Hellenic world that called war a last resort requiring conduct that would allow the restoration of peace. Aristotle argues that the cultivation of a military is necessary and good for the purpose of self-defense, not for conquering: "The proper object of practising military training is not in order that men may enslave those who do not deserve slavery, but in order that first they may themselves avoid becoming enslaved to others" (Politics, Book 7).
Stoic philosopher Panaetius considered war inhuman, but he contemplated just war when it was impossible to bring peace and justice by peaceful means. Just war could be waged solely for retribution or defense, in both cases having to be declared officially. He also established the importance of treating the defeated in a civilized way, especially those who surrendered, even after a prolonged conflict.
In ancient Rome, a "just cause" for war might include the necessity of repelling an invasion, or retaliation for pillaging or a breach of treaty. War was always potentially nefas ("wrong, forbidden"), and risked religious pollution and divine disfavor. A "just war" (bellum iustum) thus required a ritualized declaration by the fetial priests. More broadly, conventions of war and treaty-making were part of the ius gentium, the "law of nations", the customary moral obligations regarded as innate and universal to human beings.
Christian views
Christian Just War thinking is often thought to begin with Saint Ambrose, Bishop of Milan, before being developed further by his contemporary Saint Augustine of Hippo. The Just War theory, with some amendments, is still used by Christians today as a guide to whether or not a war can be justified, and how it should be fought. Christians may argue "Sometimes war may be necessary and right, even though it may not be good." In the case of a country that has been invaded by an occupying force, for example, war may be the only way to restore justice.
Saint Ambrose
Influenced by Roman law, and Cicero in particular, Ambrose believed that war was legitimate only for defensive purposes or the punishment of serious wrongdoing, and rulers were obliged to respect treaties, avoid exploiting enemies and treat the defeated with mercy. Ambrose also seems to have regarded military force as permissible against heretics, or in support of Christian orthodoxy. Nevertheless, he strictly prohibited the Church from direct involvement in violence, insisting that clergy must not take up arms themselves. Similarly, warfare had to be undertaken only to fulfill divine law, not for personal motives, and any war driven by emotional excess, vindictiveness or other disordered intentions fell outside the moral limits he envisioned.
Saint Augustine
Saint Augustine held that Christians should not resort immediately to violence, but that God has given the sword to governments for a good reason (based upon Romans 13:4). In Contra Faustum Manichaeum book 22 sections 69–76, the main source for his just war ideas, Augustine argues that Christians, as part of a government, need not be ashamed of protecting peace and punishing wickedness when they are obliged to do so. Augustine regarded intention as the main determinant of whether a war was just or sinful: "What is here required is not a bodily action, but an inward disposition. The sacred seat of virtue is the heart."
Nonetheless, Augustine asserted that peaceful inaction in the face of a grave wrong that could be rectified only by violence would be a sin. Defense of oneself or the innocent could therefore be a necessity, especially when authorized by a legitimate state authority:<blockquote>They who have waged war in obedience to the divine command, or in conformity with His laws, have represented in their persons the public justice or the wisdom of government, and in this capacity have put to death wicked men; such persons have by no means violated the commandment, "Thou shalt not kill."
But, say they, the wise man will wage Just Wars. As if he would not all the rather lament the necessity of just wars, if he remembers that he is a man; for if they were not just he would not wage them, and would therefore be delivered from all wars.</blockquote>
According to J. Mark Mattox:<blockquote>In terms of the traditional notion of jus ad bellum [the circumstances under which wars can be justly fought] ... war is a coping mechanism for righteous sovereigns who would ensure that their violent international encounters are minimal, a reflection of the Divine Will to the greatest extent possible, and always justified. In terms of the traditional notion of jus in bello [justice in war, or the moral considerations which ought to constrain the use of violence in war], war is a coping mechanism for righteous combatants who, by divine edict, have no choice but to subject themselves to their political masters and seek to ensure that they execute their war-fighting duty as justly as possible.</blockquote>
To summarize, Augustine explored the relationship between Christian charity and the use of force in greater philosophical depth than Ambrose, though he ultimately affirmed many of the same principles. Augustine did not attempt to craft a systematic doctrine of just war, and his comments on it are scattered across his writing. Even so, the foundations of what later became the classical just war tradition can be clearly identified in his thought.
For Augustine, as for Ambrose, war could also be understood as analogous to a judicial process, in which the political authority uses war to punish those who commit injustice. Indeed, he compared military action to civil litigation seeking restitution or punitive redress. Since God was the ultimate judge, and there were Old Testament precedents for His ordering of wars against Israel's enemies and unbelievers, just war could also become holy war or religious war.
Several core just war principles emerge from Augustine's writing:
Legitimate authority: Only public authorities may wage war; private individuals have no right to initiate armed conflict.
Just cause: Defense of the community, protection of allies, or redress for wrongful acts are just causes for war, though Augustine also allowed for offensive action under certain circumstances, citing Moses’ expulsion of the Amorites after they denied Israel peaceful passage.
Right intention: Proper inner disposition is essential. A ruler or soldier must act with a mindset comparable to that of a Christian judge or executioner—firm yet guided by love and compassion. Actions motivated by revenge, wrath, or greed invalidate any claim to justice in war.
Finally, the ultimate goal of just war must be to establish peace.
Saint Isidore of Seville
Isidore of Seville writes:
<blockquote>Those wars are unjust which are undertaken without cause. For aside from vengeance or to fight off enemies no just war can be waged.</blockquote>
Isidore offers a succinct definition of just war in his Etymologiae, describing it as a conflict “waged by formal declaration, either to recover seized property or to drive off an enemy”. He immediately contrasts this with unjust war, following ideas drawn from Cicero's De re publica. Although Isidore's brief, essentially Roman, formulation did not fully engage with Augustine's more sophisticated thinking, and did not fully incorporate subsequent Christian or post-Roman developments, it nevertheless became, like the writings of Saint Gregory of Tours, an important conduit through which the conception of just war entered the high medieval period, informing the Decretum of Gratian in particular.
Carolingian period
The just war ideas of Saint Augustine of Hippo and other Church Fathers were transmitted via Saint Isidore of Seville, Saint Gregory of Tours and other scholars into the Carolingian period, informing the Christianizing imperial project of Charlemagne and the consequent Carolingian Renaissance. Just/ holy war ideas about legitimate authority, just cause, punishment of enemies/unbelievers and the establishment of peace therefore gained traction, though traditional Christian concerns, particularly among clerics, about the sinfulness of killing in war, or being killed in a state of sin, were reflected in sermons, liturgies and penitential texts. Proto-jus in bello rules to protect non-combatants such as clergy, nuns, widows, orphans and the poor, including their property, also began to appear in ecclesiastical texts, as well as some capitularies (laws or ordinances) issued by Charlemagne and other rulers, anticipating the later Peace of God, and Truce of God movements.
Peace and Truce of God
The medieval Peace of God (Latin: ) was a 10th-century mass movement in Western Europe instigated by the clergy that granted immunity from violence for non-combatants.
Starting in the 11th Century, the Truce of God (Latin: ) involved Church rules that successfully limited when and where fighting could occur: Catholic forces (e.g. of warring barons) could not fight each other on Sundays, Thursdays, holidays, the entirety of Lent and Advent and other times, severely disrupting the conduct of wars. The 1179 Third Council of the Lateran adopted a version of it for the whole church.
Saint Thomas Aquinas
thumb|[[Thomas Aquinas|Saint Thomas Aquinas contributed to the development of the just war theory in medieval Europe. ]]
The just war theory by Saint Thomas Aquinas has had a lasting impact on later generations of thinkers and was part of an emerging consensus in medieval Europe on just war. In the 13th century Aquinas reflected in detail on peace and war. Aquinas was a Dominican friar and contemplated the teachings of the Bible on peace and war in combination with ideas from Aristotle, Plato, Socrates, Saint Augustine and other philosophers whose writings are part of the Western canon. Aquinas' views on war drew heavily on the , a book the Italian monk Gratian had compiled with passages from the Bible. After its publication in the 12th century, the had been republished with commentary from Pope Innocent IV and the Dominican friar Raymond of Penafort. Other significant influences on Aquinas just war theory were Alexander of Hales and Henry of Segusio.
In Summa Theologica Aquinas asserted that it is not always a sin to wage war, and he set out criteria for a just war. According to Aquinas, three requirements must be met. Firstly, the war must be waged upon the command of a rightful sovereign. Secondly, the war needs to be waged for just cause, on account of some wrong the attacked have committed. Thirdly, warriors must have the right intent, namely to promote good and to avoid evil. Aquinas came to the conclusion that a just war could be offensive and that injustice should not be tolerated so as to avoid war. Nevertheless, Aquinas argued that violence must only be used as a last resort. On the battlefield, violence was only justified to the extent it was necessary. Soldiers needed to avoid cruelty and a just war was limited by the conduct of just combatants. Aquinas argued that it was only in the pursuit of justice, that the good intention of a moral act could justify negative consequences, including the killing of the innocent during a war.
Renaissance and Christian Humanists
Various Renaissance humanists promoted Pacificist views.
- John Colet famously preached a Lenten sermon before Henry VIII, who was preparing for a war, quoting Cicero "Better an unjust peace rather than the justest war."
- Erasmus of Rotterdam wrote numerous works on peace which criticized Just War theory as a smokescreen and added extra limitations, notably The Complaint of Peace and the Treatise on War (Dulce bellum inexpertis).
A leading humanist writer after the Reformation was legal theorist Hugo Grotius, whose De jura belli ac pacis re-considered Just War and fighting wars justly.
First World War
At the beginning of the First World War, a group of theologians in Germany published a manifesto that sought to justify the actions of the German government. At the British government's request, Randall Davidson, Archbishop of Canterbury, took the lead in collaborating with a large number of other religious leaders, including some with whom he had differed in the past, to write a rebuttal of the Germans' contentions. Both German and British theologians based themselves on the just war theory, each group seeking to prove that it applied to the war waged by its own side.
Contemporary Catholic doctrine
The just war doctrine of the Catholic Church found in the 1992 Catechism of the Catholic Church, in paragraph 2309, lists four strict conditions for "legitimate defense by military force:"
- The damage inflicted by the aggressor on the nation or community of nations must be lasting, grave and certain.
- All other means of putting an end to it must have been shown to be impractical or ineffective.
- There must be serious prospects of success.
- The use of arms must not produce evils and disorders graver than the evil to be eliminated.
The Compendium of the Social Doctrine of the Church elaborates on the just war doctrine in paragraphs 500 to 501, while citing the Charter of the United Nations: